Assessment of Cadmium, Nickel and Lead Toxicity by Using Green Algae Scenedesmus Incrassatulus and Human Cell Lines: Potential In Vitro Test-Systems for Monitoring of Heavy Metal Pollution

Scenedesmus sp. as a phycoremediation agent for heavy metal removal from landfill leachate in a comparative study: batch, continuous, and membrane bioreactor (MBR)

Improper disposal of municipal solid waste led to the release of heavy metals into the environment through leachate accumulation, causing a range of health and environmental problems. Phycoremediation, using microalgae to remove heavy metals from contaminated water, was investigated as a promising alternative to traditional remediation methods. This study explored the potential of Scenedesmus sp. as a phycoremediation agent for heavy metal removal from landfill leachate. The study was conducted in batch, continuous, and membrane bioreactor (MBR). In the batch system, Scenedesmus sp. was added to the leachate and incubated for 15 days before the biomass was separated from the suspension. In the continuous system, Scenedesmus sp. was cultured in a flow-through system, and the leachate was continuously fed into the system with flow rates measured at 120, 150, and 180 mL/h for 27 days. The MBR system was similar to the continuous system, but it incorporated a membrane filtration step to remove suspended solids from the treated water. The peristaltic pump was calibrated to operate at five different flow rates: 0.24 L/h, 0.30 L/h, 0.36 L/h, 0.42 L/h, and 0.48 L/h for the MBR system and ran for 24 h. The results showed that Scenedesmus sp. was effective in removing heavy metals such as lead (Pb), cobalt (Co), chromium (Cr), nickel (Ni), and zinc (Zn) from landfill leachate in all three systems. The highest removal efficiency was observed for Ni, with a removal of 0.083 mg/L in the MBR and 0.068 mg/L in batch mode. The lowest removal efficiency was observed for Zn, with a removal of 0.032 mg/L in the MBR, 0.027 mg/L in continuous mode, and 0.022 mg/L in batch mode. The findings depicted that the adsorption capacity varied among the studied metal ions, with the highest capacity observed for Ni (II) and the lowest for Zn (II), reflecting differences in metal speciation, surface charge interactions, and affinity for the adsorbent material. These factors influenced the adsorption process and resulted in varying adsorption capacities for different metal ions. The study also evaluated the biomass growth of Scenedesmus sp. and found that it was significantly influenced by the initial metal concentration in the leachate. The results of this study suggest that Scenedesmus sp. can be used as an effective phycoremediation agent for removing heavy metals from landfill leachate.

Cytotoxicity analysis of pre- and post-hurricane harvey soil samples collected from greater houston bayous

Rapid urbanization, anthropogenic pollution and frequent flooding events are affecting the soil and water quality along the streams and bayous of Houston. Soil acts as sink and reservoir of heavy metals and nutrients affecting human and animal health. The objectives of the study are 1) to analyze the effects of the metal and nutrient concentration of bayou flood plain surface soil samples on the gut cell cytotoxicity and 2) to evaluate the spatial and temporal difference in soil contamination on cell viability of colon cancer (HT-29) and normal colon epithelial (CCD 841 CoN) cell lines. To evaluate soil contamination between pre- and post-hurricane (Summer and Fall) conditions in six Bayous (Brays, Buffalo, Halls, Hunting, Greens and White Oak Bayous) of Harris County, Texas, in vitro bioassay analysis was applied to soil extracts. The MTT assay determined that, with increase in concentration of Bayou soil from 12.5% to 100%, the viability of CCD 841 CoN and HT-29 cells decreased significantly, across all sampling locations during both summer and fall seasons. Among all the bayous, the viability of CCD 841 CoN cells in summer and fall followed the pattern of White Oak > Greens > Halls > Brays Bayou, where the viability of cells exposed to White Oak soils was 3-4 times higher than cells exposed to Brays Bayou soil at 100% soil concentration. The viability of HT-29 cells in both seasons followed the pattern of Greens > White Oak > Halls > Brays Bayou, where the viability of cells exposed to Greens Bayou soil was more than 3-4 times higher than the cells exposed to Brays Bayou soil at 100% concentration. The higher concentration of metals and nutrients such as P, Zn, Cd, and Cu might have contributed to the significant cell lethality in Brays Bayou samples compared to other locations.

Bioremediation of heavy metals using microalgae: Recent advances and mechanisms

Five heavy metals namely, arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb) and mercury (Hg) are carcinogenic and show toxicity even at trace amounts, posing threats to environmental ecology and human health. There is an emerging trend of employing microalgae in phycoremediation of heavy metals, due to several benefits including abundant availability, inexpensive, excellent metal removal efficiency and eco-friendly nature. This review presents the recent advances and mechanisms involved in bioremediation and biosorption of these toxic heavy metals utilizing microalgae. Tolerance and response of different microalgae strains to heavy metals and their bioaccumulation capability with value-added by-products formation as well as utilization of non-living biomass as biosorbents are discussed. Furthermore, challenges and future prospects in bioremediation of heavy metals by microalgae are also explored. This review aims to provide useful insights to help future development of efficient and commercially viable technology for microalgae-based heavy metal bioremediation.